View Full Version : what is a 2 step rev limiter


muscl car
01-02-2010, 08:33:14 PM
pardon my ignorance as i've been out of drag racing for 27 years !!!:eek::eek: ....but i kept hearing car at the drag races today sounding like they're tapping the rev limiter with the transbrake activated and i was told that's the sound of a step being activated .what is the actual purpose of a two step limiter and what is it for ???

back in 1983 when the last time i competitively drag raced :eek: we just foot braked or used the line lock to launch the car

KylePBZ
01-02-2010, 09:57:45 PM
The 2-step is just a box that plugs in your 6AL and has two rev limit pills in it. 1st step is your launch, usually between 3500 and 5500 give or take on what the car likes. It's activated off of the trans brake activation. 2nd step is your normal high limit chip.

http://www.summitracing.com/parts/MSD-8739/

mrdragster1970
01-02-2010, 10:03:31 PM
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The MSD soft touch style skips random cylinders from firing to keep the engine at a set RPM.
The old style would skip all the cylinders until the engine drops down to the set RPM.
The old style sounded a lot more like the engine was about to explode.

If you watch my video, it doesn't sound that rough when it launches.

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vegas1974z28
01-04-2010, 11:05:27 AM
it is for consistent launches.....bracket racing style :)

JONESYFXR
01-04-2010, 11:26:25 AM
it is for consistent launches.....bracket racing style :)

Yes it is. As stated, the rev limiter is pre-set by the user for a certain rpm. You can dial-in your launch rpm for track conditions, etc. The MSD 6AL2 has a built in soft touch two step rev limiter. The limiter drops certain cylinders on one cycle, then fires them on the next to prevent load-up.

This is what's going into my car. Very easy to hook up to either your trans-brake of rol-control button, then when the button is off the second rev limit takes over.

On the MSD website there is a cool way to us the limiter for a stick shift car, so you can hold the throttle to the floor, but when you depress the clutch the limiter kicks in. It's a pretty slick install....check it out.

http://www.msdignition.com/instructiondownload.aspx

bigbear40
01-05-2010, 09:12:23 PM
Sorry for intruding in your thread but, I dont understand why u would need the two step along with a trans brake? Cant the driver just hold the trans brake to whatever rpm he wants to launch at?

Or am i understand correctly, the first rev limiter is active so the driver can hold the gas pedal all the way to the floor and the engine will only rev to a certain rpm therefore allowing the driver to launch his car at the exact same rpm every pass. Then the second rev limiter kicks in when the trans brake is released so the engine can rev to the maximum rpm.

Do I have it correct.

Thanks.

mrdragster1970
01-05-2010, 09:29:21 PM
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Yes you do. Some of us even have 4 steps built in.

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bigbear40
01-05-2010, 10:39:37 PM
OK cool, thanks for reading to make sure i was correct in what i was saying.

What do you need 4 steps for? and would that be just an additional plug in to the msd box or do they make the one plug in with the 4 steps in it?

Thanks.

mrdragster1970
01-06-2010, 01:36:01 AM
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Most people use 3 stages of rev control, burnout, launch & top end.
I heard some people use another limiter for max rpm on the burnout, after you release the line lock.
On my cars, I have the burnout chip higher than I do the burnout as a safety.
I do my burnout by feel. Some guys can't control it, and need another chip.

Like when you see a guy that can't get up on the tire fast enough and either kills it or drives through the water.

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bigbear40
01-06-2010, 07:19:31 PM
Is there 4 individual chips if you have a 4 step?

Is there a button that lets you pick which number step you want so u can pick the burnout step, then launch step, then top end step?

Thanks again.

mrdragster1970
01-06-2010, 09:44:26 PM
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Depending on the box, determines what wiring you need. My 7-3 box has a always on step, and the rest are triggered.
We always tie into what you are trying to do. Like one step is on when the linelock is triggered,
one step is triggered when the brake is on, ect ect. Each step uses it's own chip, dial, or program.
You determine what you want to limit, and you get the box or accessories you need and wire them up.

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bigbear40
01-06-2010, 10:11:32 PM
thank you.